Conservation and restoration of endangered aquatic macrophytes in brackish water zones

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In brackish Lakes Shinji and Nakaumi and its adjacent water bodies, we found several endangered species such as Ruppia maritima, Zannichellia palustris, Potamogeton pectinatus, Carex rugulosa, Potamogeton Panormitanus, Zostera japonica and Chara corallina var. kyushuensis. Although their conservation and restoration are currently needed, little is known for their life history traits. We thus started the observation on the life cycle and growth characteristics of two species, one Zostera japoncia, a seagrass growing in brackish water zones and the other Carex rugulosa, a brackish wetland plant. Concernign Z. japonica, it was shown that (1) the maximal depth limits relative to minimal light requirements was estimated to be 30% of the irradiance at the surface, provided that Secchi depth of the observation site was c.1.5m, (2) seasonal pattern of rhizome elongation rate was determined and maximum growth was observed during September-October when water temperature was 20-25 ℃, and the plant ceased to grow when water temperature decreased below 15 ℃, and (3) the plant was eurytopic against salinity. Concerning C.rugulosa, no germination was found under the dense canopy and population was maintained by the rhizome growth. It was estimated that the belowground biomass of this plant will decrease in competition with Phragmites australis due to the shading. We also examined the allozymic variation of several endangered aquatic macrophytes including these two plants in order to know the reproductive properties and effects of wave forces and transmitted waves on Z. japonica are also observed experimentally.